A number of approaches to control the magnitude of voltage spikes generated during commutation of a current source inverter have been known heretofore.
One means for doing this has been with the use of a resistor-capacitor clamp. While this technique might be comparable in size and cost to the resistor clamp hereinafter described, it has the disadvantage that its reliability is poor because a very large number of electrolytic capacitors are required to effectively snub voltage transients. Electrolytic capacitors are unreliable in applications where they require continuous charging and discharging. In addition, this type of device is always connected to the drive output and continuously dissipates power which results in a degradation of overall system efficiency and performance.
Another means for doing this has been by use of a line commutated inverter. While this technique may have similar performance as compared to the resistor clamp hereinafter described, and has the added advantage of being non-dissipative, it has the disadvantage in that it requires a substantially larger number of parts and controls with consequent increase in size and cost.
A third approach in solving this problem has been by the use of power zener diodes. While this approach is comparable in performance and size to the resistor clamp hereinafter described, and its reliability is excellent since it has no controlled elements as does the resistor clamp, nevertheless it has the disadvantage that a power zener diode clamp is very expensive.
Still another approach that has been used is what might be called reduced drive performance in which the current source inverter would have no voltage clamp at all or a minimal voltage clamp. While this approach has good reliability as well as minimal size and cost, it nevertheless has the disadvantage that it cannot achieve large dynamic responses nor can it tolerate overload conditions. Therefore, system performance of this type of drive is severely limited.